A. Field of the Invention
The present invention generally relates to devices and methods for locating faults in electrical power cables and, more particularly, to a fault locator of the earth potential gradient type for locating faults in underground electrical power cables.
B. Description of the Prior Art
Underground or buried electrical power cables often develop faults in which the insulation of the power cable is damaged and provides a low electrical resistance path to earth ground for the electrical power flowing through the power cable.
Many devices are currently available to locate the disposition of underground electrical power cables in the earth and to locate a fault along the length of the electrical power cable. One well known type of fault location device is generally referred to as an earth potential gradient fault location device. With this device, an electrical pulse from a pulsing unit is injected into the faulted power cable to subsequently exit through the fault into the earth and back to the pulsing unit. The pulse of current through the earth establishes a voltage drop across its path of travel through the earth. A potential difference normally exists across two points in the earth and may be monitored by a monitoring unit. The monitoring unit may include a galvanometer with a meter needle that deflects to indicate the location of the fault.
An example of a prior art earth potential gradient electrical fault locator is a model 412 Fault Finder manufactured and sold by Radar Engineers, Inc. Examples of other types of fault location apparatus include a device disclosed in U.S. Pat. No. 3,299,351; a device manufactured and sold by Associated Research, Inc. identified as model No. 8500; and a device manufactured by Jay Industries identified by the name THE PINPOINTER.
Typical pulsing units used in prior art earth potential gradient fault locators generally are powered by 110 volt A.C. power supplies or 12 or 18 volt D.C. battery power supplies. Both of these types of power supplies require voltage converters to provide high voltage output pulses from the pulsing units. Typical voltage converters, for example, transformers or transistor inverters, are expensive, heavy and/or inefficient.
In addition, many of the prior art fault locating devices are characterized by relatively low voltage sensitivity and by manual controls for obtaining meter needle centering and the desired sensitivity. Prior art fault locating devices that include one or more remote probes that are inserted into the earth require an operator to expend much energy and time in repeatedly inserting the probes into the earth. In addition, typical prior art fault location devices include long cables for connecting remote probes to a fault locator meter. These long cables tend to become attached to miscellaneous debris and shrubbery present in the area of the fault. In addition, an operator becomes unnecessarily encumbered by the long cables in removing and reinserting one or more remote probes while simultaneously transporting a fault locator meter. Finally, prior art devices are generally relatively ineffective in locating faults under paved surfaces.